Air purification, including individual and collective protection filtration, is of major concern to the military, first responders, and industrial workers. Filters typically containing activated, impregnated carbons are employed to filter toxic chemicals, and have limited lifetimes after exposure. Furthermore, due to interaction with environmental contaminants, such as low level concentrations of SOx, NOx, hydrocarbon vapors, etc., the capacity of filters can degrade even before a toxic chemical event.
Colorimetric sensing of toxic chemicals, such as chemical warfare agents and narcotics, is of major concern to the Department of Defense community, military, and first responders. In-place chemical sensors, such as M8 or M9 paper and the volatile organic compounds (VOC) test kit, can identify neat toxic chemicals, or more specifically chemical warfare agents, in the liquid phase only.
In individual protection having an end-of-service-life indicator (ESLI) that tells the user when the filter has run out of protective capability is a major development thrust, and a need for the community. Here, an ESLI should interact/react with toxic chemicals such that a response (ideally visible, but not necessarily) occurs. There are ESLI technologies currently being fielded; however, there are severe shortcomings to these, such as poor sensing of reactive gases or insufficient reactivity.
Due to continuous operation of filtration and sensing devices, ambient and battlefield contaminants (BFCs) decrease physical adsorption and chemical reactivity of the filter material over time due to interactions with the active sites associated with the material contained within the devices. Interactions can also occur with the pore structure and/or the impregnants associated with the filter material contained within the filter housing, such as for example activated carbon impregnated with salts of copper, zinc, molybdenum and silver, plus triethylenediamine. Residual life indicator (RLI) technologies have been developed; however, most do not accurately determine the effects of acidic/acid-forming contaminants on the residual life of the filtration media.
As such, new processes are needed for the detection and quantification of acidic/acid-forming contaminants that may be employed to determine the residual life of a filtration system.